This project develops new statistical methods for epidemiology with broad applications and also methods as needed for ongoing projects in epidemiology, particularly those related to reproductive studies. The work this year focused on the theory of directed acyclic graphs, an important mechanism for building models appropriate for assessing the adjusted causal effect of a factor on disease risk. An extension was proposed whereby synergism can be represented, both for pure interaction scenarios (as with PKU) and for statistical interactions that can depend on scale. In other work collaborative with Allen Wilcox of the Epidemiology Branch, we have updated our chapter on reproductive epidemiology for the textbook entitled Modern Epidemiology, by Rothman, Greenland and Lash.